1. Field of the Invention
The present invention relates to a display pattern processing apparatus, and more particularly to a color pattern processing apparatus having a video memory into which is written color pattern data which is to be displayed on a display such as a cathode ray tube (CRT).
2. Description of the Background Art
Color data to be displayed on a CRT generally is written first into a video memory which is a random access memory (RAM) in accordance with a pre-edit operation. Thereafter, the color data is converted into a video signal and is sent to the CRT. The number of bits which may be stored in the video memory usually is at least as large as the number of picture elements on a CRT screen. In a color display, three video memories are required, for red (R), green (G), and blue (B), respectively. Color data corresponding to one picture element, then, consists of three bits, one red, one green, and one blue. A color to be displayed is determined in accordance with a combination of these bits.
Thus, eight colors, as indicated in Table 1 on the next page, may be displayed according to the combination of the red, green, and blue bits.
TABLE 1 ______________________________________ R G B Color ______________________________________ 1 0 0 Red 0 1 0 Green 0 0 1 Blue 0 0 0 Black 1 0 1 Magenta 1 1 0 Yellow 0 1 1 Cyan 1 1 1 White ______________________________________
Display pattern data and a color code are required for a color display. The color code consists of three bits (R, G, B) as described above, and is assigned to each item of pattern data. The color code is designated by an operator and is written into the video memories.
In multicolor displays, it has been known to execute a writing operation to the video memories for each of the colors to be displayed. For example, when two colors (such as red and black) are to be displayed, a color code for one of the two colors first is written into all of the video memories. Thereafter, the other color code is written. That is, a red color code "1 0 0" first is written into all locations in the video memories. Then, every location where a black color code "0 0 0" is to be written is changed to the black color code. Therefore, at least two writing operations must be performed for a two-color display. If more than two colors are to be displayed, one writing operation must be performed for each color to be displayed. These writing operations require much time.
Further, digital pattern processing, such as filing for changing luminance, or masking has been proposed. To perform digital pattern processing, a logical operation (AND, OR, EXOR, and the like) is required. It has been known to perform such a logical operation after writing the appropriate color codes into the video memories. Therefore, reading of the color data written into the video memories, a logical operation according to the desired digital pattern processing, and a writing operation of the result of the logical operation into the video memories also are required.